1. Field of the Invention
The present invention relates to a growth method of a polymer film and, more particularly, to a method of producing a functional organic polymer film for insulating between multi-layer wirings of a semiconductor integrated circuit.
2. Description of the Prior Art
As semiconductor integrated circuits have been reduced in size deterioration of performance caused by wiring signal delay becomes a problem. Wiring signal delay of the semiconductor integrated circuit depends upon a time constant on interconnection CR (C: interconnection capacity, R: interconnection resistance). However, there is a fear of a state where the constant on interconnection CR can not follow an improvement in switching rate of a transistor because of an increase in interconnection resistance caused by a reduction in line width and an increase in capacity between wirings caused by a reduction in line space. Although an aluminum alloy is used as a wiring material of the semiconductor integrated circuit at present, copper wiring or silver wiring is now under study to reduce the interconnection resistance.
On the other hand, an insulating film material having a dielectric constant lower than that of a silica (SiO.sub.2) insulating film used at present is also under study to reduce the capacity between wirings. As the insulating film material having low dielectric constant, for example, fluorine-containing silica (SiOF), porous silica and an organic polymer film (organic insulating film) are known. The fluorine-containing silica has a problem that a wiring metal is corroded with hydrofluoric acid produced by the reaction between fluorine and water or between fluorine and hydrogen in the film, and that the dielectric constant increases by eliminated fluorine. The porous silica is expected in that the dielectric constant is not more than 2.
However, there are some cases where the dielectric constant increases by water condensation in micropores and a break down voltage is lowered. It is lately of urgent necessity to develop an organic polymer film having excellent thermal stability and moisture absorption resistance as an interlayer insulating film for insulating between multi-layer wirings on the semiconductor integrated circuit. With respect to the moisture resistance, it is essential that a hydrophilic group is not contained in the organic monomer and it is desired that the condensation polymerization reaction releasing water is not included in the polymerization reaction from the organic monomer.
The term "organic monomer" in this specification refers to those wherein the polymerization reaction of the organic monomer as a constituent unit occurs to form an organic polymer.
The growth method of such a functional organic polymer film includes a spincoating method of an organic monomer. This spincoating method is a method used widely in the growth of the organic polymer film. In this method, the organic monomer is dissolved in a solvent. The organic monomer dissolved in this solvent is coated on a substrate by the spincoating method. Thereafter, the solvent is removed and the polymerization reaction of the organic monomer proceeds by heating, thereby to form a film on the substrate. As a result, a film having a two-dimensional or three-dimensional network structure, or a polymer film is formed. That is, the structure of the organic monomer becomes a skeleton constituting an organic insulating film as the formed polymer film.
For example, "REAL-TIME FT-IR OF THE REACTION KINETICS FOR THE POLYMERIZATION OF DIVINYL SILOXANE BISBENZOCYCLOBUTENE MONOMERS (Material Research Symposium Proceeding Vol. 227, p. 103, 1991) T. M. Stokich, Jr. W. M. Lee, R. A. Peters (hereinafter referred to as a "reference 1") describes about a growth method of an organic polymer film, using a divinyl siloxane bisbenzocyclobutene monomer (hereinafter referred to as a "DVS-BCB monomer"). ##STR1##
After a dissolved material obtained by dissolving a DVS-BCB monomer in mesitylene is spincoated, mesitylene as the solvent is removed by baking at 100.degree. C. and the residue was further heated to 300-350.degree. C., whereby a carbon four-membered ring in benzocyclobutene causes the thermal ring-opening polymerization reaction and an organic polymer film (hereinafter referred to as a "DVS-BCB polymer film"),wherein a derivative of DVS-BCB represented by the following chemical formula as a principal skeleton grows. ##STR2##
The present inventors have suggested an evaporation method of an organic monomer as the growth method of a functional organic polymer film in JP-A-11-017006. This method is a method of vaporizing an organic monomer and polymerizing the monomer on a substrate in the vapor phase, thereby to obtain an organic polymer film. In FIG. 13, an organic film growth system by direct vaporization of this organic monomer is shown. An organic monomer 1 in a tank 17 is evaporated by heating under reduced pressure. A reaction chamber is connected with an exhaust pump 10 through an exhaust gas piping 40 and the evaporated organic monomer is supplied to a reaction chamber 11 through a vaporized raw material piping 35 by evacuating inside the reaction chamber 11. The organic monomer molecules are adsorbed on the surface of a semiconductor substrate 14 on which a semiconductor integrated circuit is formed. Furthermore, the polymerization reaction proceeds by thermal energy supplied by a substrate heating portion 15, thereby to form an organic insulating film 13.
The spincoating method described above has a drawback that the yield of the organic film is low because about 90% of the dissolved material is scattered from the substrate.
This method is a method of heating a spincoated film in a baking furnace thereby to remove a solvent first, and heating to high temperature to cause the polymerization reaction of the organic monomer thereby to form an organic polymer film. When oxygen is present in the baking furnace, the desired organic polymer film is not obtained sometimes by reacting oxygen with a portion of the organic monomer.
For example, a permissible oxygen concentration, in the case where the dissolved material obtained by dissolving a DVS-BCB monomer in mesitylene is spincoated and then baked, is not more than 100 ppm. For this reason, the atmosphere in the whole baking furnace must be replaced by a nitrogen gas and it is difficult to realize at low cost.
Since the dissolved oxygen in the solvent is sometimes reacted with the organic monomer during baking, precise atmosphere control is required, but it is difficult to control the oxygen concentration in the spincoating method.
Although the spincoating is conducted in a locally evacuated spincoating chamber, there is also a risk of contamination of the spincoated film with floating dust particles or fine particles of the dried organic monomer adhered to the inner wall of the spincoating chamber. In this case, the quality of the film is deteriorated. Furthermore, the spincoating also has a problem that the environmental burden is large because a large amount of an organic solvent is required.
The growth method of a functional organic polymer film by directly vaporizing an organic monomer, which is disclosed in JP-A-11-017006 by the present inventors, was superior in that the yield of the organic film is more better than that of the spincoating method. However, since a method of vaporizing the organic monomer from a vapor-liquid interface is employed, the vaporization of the organic monomer depends largely on a vapor pressure of the organic monomer and the organic monomer must be heated to high temperature. On the other hand, since the organic monomer has reactivity, the polymerization reaction also proceeds at high temperature and the vaporization of the organic monomer has a tendency to be unstable, sometimes. Therefore, an improvement has been required.